The present invention relates generally to improvements in automatic locking safety belt retractors used in vehicles and it relates more particularly to an improved acceleration responsive automatic locking belt retractor provided with a mechanism for sensing the change of movement of a vehicle and locking the seat belt against extraction in response to a predetermined acceleration.
There are various types of conventional vehicle safety or restraint belt retractors which lock a seat belt in response to a sharp change in the speed of the vehicle when it collides with an object. In conventional retractors, however, the acceleration sensitivity is very high and the acceleration sensing mechanism is repeatedly actuated and deactuated at a high frequency. Consequently, for example, in a mechanism in which a ratchet wheel rotating with the belt retraction reel is with a pawl to lock the reel and seat belt, it occasionally happens that the tips of the teeth of the ratchet wheel and the pawl tooth or tip are momentarily in the same position. In such an event, the tips of the ratchet wheel teeth, the rotational speed of which has been greatly increased by the belt withdrawing force outwardly kick or impel the pawl tooth so as to prevent the pawl from engaging the ratchet wheel. As a result, the belt is withdrawn a considerable and excessive amount by the time the pawl has returned to a proper position where it can engage the ratchet wheel. The above occurrence substantially prevents the proper and reliable functioning of the seat belt. In some cases, the teeth of the ratchet wheel or the pawl tooth are damaged to thereby prevent a complete and proper engagement therebetween.
The applicant, in co-pending U.S. application Ser. No. 901,049 filed Apr. 28, 1978 now U.S. Pat. No. 4,150,799 proposed an automatic locking retractor reel in which the above-mentioned drawbacks encountered in conventional reels are eliminated and in which a pawl is not employed. Such an acceleration responsive automatic braking safety belt retractor includes a mounting bracket having opposing side plates between which is journalled a shaft carrying a belt retraction wheel betwen the side plates and a ratchet wheel along the outside face of a first plate. A guide plate is affixed to the first plate outside face and has a circular opening registering with the ratchet wheel periphery and a linear guide slot vertically tangent to the opening and terminating at its top in a transverse stop shoulder and communicates along its upper inner side with the opening the lower part of the communication being delineated by an outwardly downwardly inclined second stop shoulder. A stop member is longitudinally slidably engaged and depends from the slot and is provided with an inwardly directed projection having an arcuate upper edge and a bottom edge parallel to the second shoulder. A lever engages the stop member bottom edge and is swung upwardly by an acceleration actuated pendulum to raise the stop member and bring the projection into engagement with the ratchet wheel to brake it and the reel. While the aforesaid retractor is highly satisfactory, it possesses important drawbacks, among which is lack of great durability and frequent impairment of operation following long use.